1. Field of the Invention
The invention relates to a process for synthesizing alkylated tannin Mannich polymers and the use of these polymers in a process for removing color contaminants from waste water.
2. Description of the Prior Art
The removal of color from the effluent streams of papermills continues to be a problem within the pulp and paper industry. It is necessary that these downstream waste waters be treated for color removal prior to discharge into public water ways. Increasingly, there has been concern about the possible toxic effects of colored waste discharge water causing reduced levels of oxygen concentration in effluent waters, and creating oxidation products which may be potentially harmful. Prior art solutions to the color removal problem have included the use of tannin based flocculant compounds.
Tannins are plant extracts that can be subdivided into two types, hydrolyzable and condensed, based on their structure. Hydrolyzable tannin extracts are comprised of relatively low molecular weight compounds comprised of esters of a sugar with trihydroxybenzenecarboxylic acids. Condensed tannin extracts are a complex mixture comprised of about 70% polyflavinoids. Formula 1 shows the structure of the main flavinoid unit present in wattle tannin, a mimosa bark extract. This flavinoid is thought to form two to eleven-unit oligomers by self-condensation at positions 4 and 6 to give wattle tannin, which possesses a number average molecular weight of 1250. ##STR1##
Tannins also undergo Mannich aminomethylation by reaction with an aldehyde and an amine. The resulting "tannin Mannich" polymer possesses a higher molecular weight due to formaldehyde and Mannich base crosslinking, and also possesses ampholytic character due to the presence of both cationic amines and anionic phenols on the polymers. As a result of their ampholytic nature, tannin Mannich polymers are highly water soluble at extreme pH's, but are often insoluble at pH's near 7 because this is near their isoelectric point (where the net charge on the polymer is zero). Tannin Mannich polymers continue to crosslink upon storage until they eventually form an insoluble gel. This continual crosslinking limits their shelf life to about three months.
Tannin Mannich polymers have been used in South Africa for many years as a flocculant for clay suspensions in municipal water treatment. In North America, Dearborn Chemical Company sells a "Klar-Aid.RTM."series of tannin Mannich polymers for water clarification. Tannin-based materials have also been claimed for other water treatment applications. The mechanism by which tannin Mannichs are presumed to work for water clarification relies upon their relative insolubility at neutral pH, which causes them to self-flocculate and sweep other suspended particulates out of the water as they settle.
Representative tannin Mannich polymers include those produced according to the process disclosed in U.S. Pat. No. 4,558,080, (the Dearborn process) the disclosure of which is incorporated herein by reference. Unfortunately, the use of these color removal compounds is limited with respect to the pH range of waste water with which they may be used. Tannin Mannich polymers do not perform well for color removal from kraft papermill waste streams unless the pH of the waste stream can be lowered. Under these conditions, colors are removed effectively, but high doses of the polymer are required.
Desirably, a compound which can effectively remove color from waste water effluent streams and which is effective within a wide range of pH would exist.